1. Field of the Invention
The present disclosure relates to an image coding apparatus and an image coding method for adaptively estimating an intra prediction direction.
2. Description of the Related Art
In recent years, the H.265/HEVC (High-Efficiency Video Coding) standard has been developed as a new image coding standard (NPL 1 of Non-Patent Literature). The HEVC standard prescribes 35 prediction directions in intra prediction of a block (FIG. 1A) (for example, 33 ordinary prediction directions, one DC prediction direction, one planar prediction direction). In order to determine one prediction direction from 35 prediction directions, image coding apparatuses perform coding by using all the prediction directions. The image coding apparatuses then compare rate distortion optimization values in respective prediction directions to select the prediction direction in which the optimization value is smallest. In this way, performing coding in all the prediction directions and comparing the rate distortion optimization values will lead to higher coding efficiency, but on the other hand, to a larger amount of processing in performing coding.